Ultrasonic Particle Manipulation in Glass Capillaries: A Concise Review

Abstract

Ultrasonic particle manipulation (UPM), a non-contact and label-free method that uses ultrasonic waves to manipulate micro- or nano-scale particles, has recently gained significant attention in the microfluidics community. Moreover, glass is optically transparent and has dimensional stability, distinct acoustic impedance to water and a high acoustic quality factor, making it an excellent material for constructing chambers for ultrasonic resonators. Over the past several decades, glass capillaries are increasingly designed for a variety of UPMs, e.g., patterning, focusing, trapping and transporting of micron or submicron particles. Herein, we review established and emerging glass capillary-transducer devices, describing their underlying mechanisms of operation, with special emphasis on the application of glass capillaries with fluid channels of various cross-sections (i.e., rectangular, square and circular) on UPM. We believe that this review will provide a superior guidance for the design of glass capillary-based UPM devices for acoustic tweezers-based research.

Sub-wavelength acoustic stencil for tailored micropatterning

“…Each of these D values (from 15 μm to 35 μm) is well below the acoustic wavelength in the fluid (≈250 μm at 5.8 MHz), evidencing the sub-wavelength nature of this trapping behaviour, and demonstrating the flexibility of stencil-based trapping compared to previous acoustofluidic implementations in which patterns are limited to half-wavelength periodic lines and grids. 48–50 Fig. 4a–e shows patterning effects in the case of a constant S = 20 μm with D between 15 and 30 μm.…”

Acoustic Manipulation of Particles in Microfluidic Chips with an Adaptive Controller that Models Acoustic Fields

“…This contrasts with black-box models, such as neural networks, [42,54,55] which can be difficult to interpret and therefore it is difficult to understand why the controller acts the way it does. However, some caution in interpreting the models is in order: any other phenomena transporting the particles, such as acoustic streaming [56][57][58] or fluid flows, [59] will affect the modeling results. In our case, our particles were relatively large, so the drag force from acoustic streaming can be assumed to be insignificant, and the pump was turned off to ensure that the fluid did not flow during manipulation.…”

Acoustofluidic Patterning inside Capillary Tubes Using Standing Surface Acoustic Waves

“…Microfluidic elements, i.e., microchambers and microchannels, are usually fabricated in a clean-room environment using materials such as polydimethylsiloxane (PDMS) [3-5, 8,9], silicone elastomer [15], polymethyl methacrylate (PMMA) [16,17], or glass [7,18,19]. Alternatively, capillary tubes have also been integrated with acoustic devices and used to trap [20][21][22][23][24][25][26][27][28], focus [29][30][31][32][33][34][35], align and pattern [36][37][38][39][40], separate [41,42], deform [43], enrich [44,45], arrange [46], and manipulate [47] microparticles and biological cells [48]. For example, Lata et al [36] and Lisa et al [46] used capillary tubes to immobilise biological cells in a cured gel to form a fibre with fixed positions of the cells.…”

“…The capillary tubes, are generally disposable, low-cost, optically transparent, and easy to use within the acoustofluidic setups. They also offer high acoustic quality and do not require additional bonding of various acoustofluidic components [48]. They are normally made of glass [21-36, 38-41, 43-47], but sometimes polyimide [37] and cellulose [20].…”

“…They are normally made of glass [21-36, 38-41, 43-47], but sometimes polyimide [37] and cellulose [20]. Capillary tubes have various cross-section shapes, such as circular [20,21,29,31,34-36, 41,46,47], square [22,30,32,33,37,39,41,43] and rectangular [23-28, 38,40], which makes them good candidates for various acoustofluidic applications [48].…”